Paul Gascoigne, the former England footballer, is to become the latest celebrity to sue the News of the World, alleging that he was a victim of the phone-hacking scandal that has rocked Rupert Murdoch's media empire.

His solicitor, Gerald Shamash, confirmed today that proceedings would be issued within days.

Shamash claimed that Gascoigne was in a vulnerable mental state and that his recovery had been hindered because of the stress of believing that his phone had been hacked. "It has made things even more difficult for his general wellbeing," he said.

Gascoigne has been fighting drink and drug problems for years and been in and out of rehabilitation clinics.

The Observer has now established that the comedian Steve Coogan has also issued proceedings and that Chris Tarrant, the television presenter, and the jockey Kieren Fallon are expected to launch legal actions soon.

There are now at least five law firms representing alleged victims of phone hacking. Lawyers from all five have confirmed that they expect more claims to be filed in the next few weeks.

So far, four people have settled claims against the newspaper before they reached court, including the celebrity publicist Max Clifford.

The increasing number of people who are suing or threatening to sue the paper has raised fresh questions about how widespread the practice of phone hacking was on the newspaper while it was edited by the prime minister's director of communications, Andy Coulson. Senior executives on the paper maintain that the practice was the work of a rogue reporter, Clive Goodman, who was jailed in 2007 for his part in the scandal. But many believe that hundreds or even thousands of phones were hacked by a private investigator, Glenn Mulcaire, while he was working for the newspaper.

Questions are being asked about the role of the Metropolitan police, which was obliged by the Crown Prosecution Service to inform suspected victims that their phones had been hacked.

Paul Farrelly MP, a member of the parliamentary culture, media and sport select committee that conducted an investigation into the allegations, said he was concerned that the Met had adopted a new policy towards requests for information from suspected victims.

Previously someone could request that the Met scour its files to establish whether their phone had been hacked. Now Scotland Yard asks for a suspected victim to outline on what grounds they believe their phone has been hacked before making a search.

"We found great fault with the police investigation and to that we can add the conduct of the Crown Prosecution Service [CPS], which simply rubber stamps the Met's totally inadequate handling of the affair," Farrelly said.

John Kelly, of the law firm Schillings, who is representing a number of people seeking damages from the newspaper, said it was important that a comprehensive list of victims was established.

"Unlawfully intercepting phone calls is a massive invasion of privacy," Kelly said. "We will not know the full extent of how widespread this activity was until we know exactly who was targeted. It's in everybody's interest for the Met and News Group to let people know if they may have been a victim. In the meantime, more claims will continue to be brought."

In answer to a freedom of information request, Scotland Yard has confirmed only that there were 91 individuals whose pin numbers, for their mobile phone message services, were found in material seized from Mulcaire.

In a sign of the growing disquiet at the Met's handling of the investigation, the director of public prosecutions, Keir Starmer, announced on Friday that the CPS had agreed to conduct a "comprehensive assessment" of all material held by Scotland Yard relating to phone hacking.

Charlotte Harris, the solicitor representing the sports agent Sky Andrew, who is bringing a claim against the newspaper, said she trusted the assessment would be robust.

"The interpretation of whatever documents or other evidence should not be something that is done by the Metropolitan police alone," Harris said. "An independent eye is welcomed given the civil claims, the reported settlements, the suspension of Ian Edmondson and the new internal investigation by the News of the World."

News International, parent company of News Group Newspapers, said the News of the World would "continue to co-operate with any request from the police or the Crown Prosection Service".